Job site generator calculator
A circular saw and work lights need a 3,500W portable. Add the pancake compressor (1,500W running, 4,500 at start) and you're a 6,500W crew. Check only the tools that actually run in the same ten seconds, then read the panel.
Sizing for a crew without overbuying
The same-ten-seconds rule does the work. Watts only matter simultaneously; a truck full of tools that take turns is a small load with occasional spikes. So the realistic worst case on most residential sites is one saw in the cut, the compressor starting, and the lights on, which the default checklist above prices at a 6,500W class. Framing crews with a table saw and a 2 HP compressor go one size up.
GFCI matters more than watts on paper. OSHA sites want GFCI-protected receptacles, and many open-frame units have bonded neutrals that trip external GFCI cords in confusing ways. If the generator will feed a subpanel or a spider box, that conversation belongs to whoever stamps the temporary power permit, not this page.
Questions people ask
What size generator for power tools?
One saw plus lights runs on a 3,500W portable: a 7-1/4 inch circular saw draws about 1,500W and doubles at start. The class jumps fast with compressors, because a pancake compressor’s induction motor starts at three times its 1,500W run figure. A two-man crew running a saw and a compressor together is squarely in 6,500W territory.
What size generator runs a welder?
For a 120V stick or MIG box, a 5,000W portable is the floor and 6,500 is comfortable. Welders also care about waveform: a cheap open-frame unit with wobbly voltage makes ugly beads. If the welder is the main event, size the generator to the welder manual’s generator-rating line, which usually says twice the welder’s rated draw.
Do I count every tool on the truck?
Count what runs in the same ten seconds. A framing crew’s saw, a trim carpenter’s miter box, and the compressor never all cut at once; typically it is one saw, the compressor kicking in, and the lights. Check exactly that set. Oversizing a jobsite unit costs you every morning you lift it onto the tailgate.